The technical field of this disclosure is belt driven power transfer devices, particularly, a belt tension/drive for a pinch roller system.
Pinch roller systems are used with machines that handle sheets of material, such as a paper folder. Paper folders are able to take sheets of paper or other material and fold them into various patterns for stuffing in envelopes or mass mailings. To accomplish the folding, the paper folder feeds paper between a pinch roller and a capstan roller. The paper path is blocked, so that the travel of the paper is stopped and the paper buckles. A second path is provided where the buckles occurs, so the blocked paper follows the second path. As the paper travels into this second path, it is grabbed by a second pinch roller and the original capstan roller, which creases the paper at the point of buckling, and drives the paper through any remaining fold processes. The blocking, grabbing, and creasing process can be repeated to form multiple folds.
The pinch rollers must be urged toward the capstan roller, while having sufficient freedom of movement to allow for single and multiple sheets of paper of various weights to pass between the pinch rollers and the capstan roller. It is very important that all of the rollers continually driver the paper through the folder. Large degrees of paper slippage cannot be tolerated, as this will cause a bad fold and/or a paper jam. Therefore, not only do the pinch rollers have to be urged toward the capstan roller, they must all be driven simultaneously at the same surface speed. Pinch roller systems typically provide separate means to perform the functions of urging the pinch rollers toward the capstan roller and driving the pinch rollers.
FIGS. 1 and 2 show the use of springs to urge the pinch rollers toward the capstan roller. The bearings and bushings used to support and guide the pinch rollers and capstan roller have been omitted from the figures for clarity. FIG. 1 shows a schematic diagram of a Single Spring Method in which a tension spring 20 is wrapped around pinch rollers 22 to urge the pinch rollers 22 toward capstan roller 24. FIG. 2 shows a schematic diagram of a Multi-Spring Method in which each pinch roller 30 is urged toward capstan roller 32 by a compression spring 34. Each of the pinch rollers 30 has a compression spring 34, increasing cost and complexity. Both the Single Spring Method and the Multi-Spring Method provide the force to urge the pinch rollers toward the capstan roller while providing sufficient freedom of movement to allow for different material thickness between the pinch rollers and the capstan roller, but require separate means to drive the pinch rollers.
FIGS. 3 and 4 show the use of gears and cogged belts to drive the pinch rollers at a simultaneous surface speed. The bearings and bushings used to support and guide the pinch rollers and capstan roller have been omitted from the figures for clarity.
FIG. 3 shows a schematic diagram of Gear Driven Pinch Rollers in which a capstan roller gear 40 attached to a capstan roller (not shown) drives pinch roller gears 42 attached to a pinch roller (not shown). Gears are designed to operate at a specific distance from one another. The point where gears make contact is commonly known as the pitch diameter. The pitch diameter for the capstan roller gear 40 and the pinch roller gears 42 must be the same as their respective roller diameters or there will be a difference in surface speeds between the capstan roller and the pinch roller. Surface speed difference causes binding and lock-up conditions. Because of gear design restrictions, there are limited options for capstan and pinch roller design.
Although the capstan roller gear 40 and the pinch roller gears 42 contact each other at the pitch diameter, a certain amount of play, also called backlash, occurs. Because the capstan roller and pinch roller move away from each other as paper passes between them, the point of contact of the associated gears moves away from the pitch diameter. This increases backlash, causing premature wear, which increases the chance that a gear could slip a tooth and cause a bad fold or paper jam.
FIG. 4 shows a schematic diagram of Cogged Belt Driven Pinch Rollers in which a cogged belt 50 is wrapped around pinch roller sprockets 52 attached to a pinch roller (not shown). Because the pinch rollers are in contact with the capstan roller, the capstan roller 54 turns the pinch roller, which turns the pinch roller sprockets 52. The teeth of the cogged belt 50 are engaged with the teeth of the pinch roller sprockets 52. To maintain the tooth alignment, the cogged belt 50 must be stiff with very little stretch or compliance. Because the capstan roller and pinch roller move away from each other as paper passes between them, the cogged belt 50 cannot be pulled tight to the pinch roller sprockets 52, but must have a certain amount of slack to allow the pinch rollers to move. The slack causes play between the teeth of the cogged belt 50 and the teeth of the pinch roller sprockets 52. Too much play can cause premature wear and slippage of the pinch rollers.
Both the Gear Driven Pinch Rollers and Cogged Belt Driven Pinch Rollers provide the means to drive the pinch rollers at the same surface speed, but require separate means to urge the pinch rollers toward the capstan roller. This increases the cost and complexity of the system. The changing distance between the capstan roller and pinch roller as paper passes between them causes tooth alignment problems and premature wear.
It would be desirable to have a belt tension/drive for a pinch roller system that would overcome the above disadvantages.
One aspect of the present invention provides a belt tension/drive for a pinch roller system which combines the tension and drive functions.
Another aspect of the present invention provides a belt tension/drive for a pinch roller system at lower cost and with less complexity.
Another aspect of the present invention provides a belt tension/drive for a pinch roller system avoiding premature wear that could cause operating and maintenance problems.
Another aspect of the present invention provides a belt tension/drive for a pinch roller system avoiding the use of gears and springs.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention, rather than limiting the scope of the invention being defined by the appended claims and equivalents thereof.